The DUCK94 Coastal Field Experiment - Overview

Introduction

Since 1979, the Coastal and Hydraulics Laboratory (formerly the Coastal
Engineering Research Center) of the US Army Engineer Waterways Experiment
Station has hosted a series of increasingly complex, multi-investigator,
multi-agency nearshore field experiments at its Field Research Facility
(FRF) located in Duck, North Carolina, USA. Three experiments, DELILAH
and DUCK94, and SandyDuck,
all evolved from scientific and pragmatic successes of prior work at this
site, and have the basic objectives of improving fundamental understanding
and modeling of surf zone physics. The emphasis in DELILAH was surf zone
hydrodynamics in the presence of a changing barred bathymetry. DUCK94 and
SandyDuck have added components to resolve sediment transport and morphologic
evolution at bedform scales from ripples to nearshore bars. DUCK94 was
designed as a pilot effort to test instruments and procedures required
for the more comprehensive SandyDuck experiment. This document summarizes
DUCK94 including participants, environmental conditions, data collected,
and data availability.

DUCK94

Success of DELILAH, and the evident need for more detailed information
about sediment transport and morphologic evolution that results from hydrodynamic
forcing, initiated interest in further field work to be supported by the
US Army Corps of Engineers, Office of Naval Research, the Naval Research
Laboratory and the US Geological Survey. A plan for two additional field
experiments developed. The first, DUCK94, was intended as a test run for
new instrumentation, a more formal experiment organization, and more complicated
logistics in preparation for SandyDuck, the second experiment. DUCK94 was
scheduled for August and October 1994 to take advantage of the synergy
offered by the National Science Foundation's Coastal Ocean Processes (CoOP)
experiment (Butman, 1994), being conducted at the FRF during that time.
The following focus topics were established as fundamental to improved
understanding of surf zone sediment transport:

Considerable interest was expressed for DUCK94. Table 1 lists the 19
organizations that participated, involving more than 100 scientists, students,
and technicians. Instrument measurements were complemented by observations
from ground- and aircraft-based radar and video systems. Table 2 lists
the 31 basic studies, along with the principal investigators, their primary
focus areas, and experiment durations. The extensive instrumentation resulted
from consideration of relevant measurement scales required to address SandyDuck
science objectives. Guidance was provided by using measured velocity data
from DELILAH and sediment transport modeling. Based on this analysis, a
general nearshore instrumentation array was designed (Birkemeier &
Thornton, 1994). The full array, shown in Figure 1, was used during the
October phase of DUCK94. An abbreviated form of this array was used in
the August segment of the experiment. Formal dates for DUCK94 were 8-24
August and 1-24 October, though some investigations (Table 2) of various
durations were underway between June and November.

A wide variety of instrumentation was used in DUCK94. Conventional total-station
surveying techniques were used in subaerial morphology studies (29, referring
to investigations by experiment number in Table 2), minigrid surveys (15),
and positioning of all stationary instruments. Central to the main layout
were cross-shore arrays of instrument clusters (11), each containing an
electromagnetic current meter, a pressure gauge, an acoustic altimeter,
and a thermometer (Fedderson, et al.,1997). The altimeters permitted the
first comprehensive real-time measurements of bottom changes (8) (Gallagher,
Elgar & Guza, 1997). A large number of suspended sediment concentration
gauges were deployed, including optical backscattering sensors (16, 22,
26, 30), and less intrusive fiber- optic backscattering sensors (1). The
Coherent Acoustic Sediment Probe (Stanton & Thornton, 1997) was mounted
on a mobile sled along with current meters, pressure gauges, scanning sonars,
and void fraction sensors (20, 25, 26). The Sensor Insertion System,

Environmental conditions during the October phase of DUCK94 are illustrated
in Figure 2. Two high-wave events occurred. The first was on 2-4 October,
wherein wave heights exceeded 2.5 m. Wave heights reached 4.5 m during
the second storm, an eight-day event beginning on 10 October. During the
larger storm, large bottom changes were accompanied by a complex nearshore
circulation pattern wherein wave-driven currents in the surf zone were
opposed by strong wind-driven longshore flows offshore. As shown in Figure
2, currents in the nearshore trough changed from about 1 m/s to the south
at the beginning of the storm on 10 October to about 1 m/s to the north
just prior to the peak of the storm on 15 October.

Figure 3 illustrates four of the 12 minigrid surveys collected during
October. Following a pattern similar to that observed in DELILAH, the bar
moved offshore and became more linear in the initial part of the 10 October
storm. High waves prevented daily surveys until 21 October, when the survey
revealed that a very large rip channel had developed. Evolution of this
channel is evident in video time exposure images depicted in Figure 4.
Sequences of profile data through the region of the rip are shown in Figure
5, where it is seen that the bar crest moved 100 m seaward, causing 1.2
m of deposition at its most seaward observed location on 18 October. By
21 October, the bar crest had begun migrating landward.

DUCK94 data are being analyzed, and research results are beginning to
appear in the literature. Preliminary findings were discussed at a post-experiment
meeting (summarized by Long & Sallenger, 1995), where adequacy of the
DUCK94 experiment plan was also evaluated in preparation for SandyDuck.

Data Availability

The investigators agreed on a data sharing policy that offers protection
of data by collecting investigators, encourages collaboration, and provides
for eventual public release. This policy is:

a. global release of all data three years after the
experiment;
b. responsible investigators will be identified when data sets
are used by others;
c. prior to three-years, data shared by agreement between individual
investigators;
d. any manuscript based on shared data must be approved by all
responsible investigators prior to submission;
e. no third-party data dissemination;
f. principal investigators control use of their data.

The DUCK94 data are now available from the DUCK94
Data Server. The server provides easy access to the
data through a html browser or ftp. Much of the data are in the form
of processed statistics with some "raw" time series data are available
as well. The majority of the "raw" data will be included by summer
2001. A discussion of the individual DUCK94
experiments, including tables listing sensors, data sets, and a summary
of results, findings and publications, are available through this web link.